The construction industry has seen an increase in the use of engineered wood products (EWP) in building projects. EWP members differ from conventional wood products in that EWP members are fiber-glue composites. I-beam type EWP members typically have flange members of solid cut wood and web members of composite wood. EWP members also include rectangular beams formed of lumber strips or veneers glued together. These products are known as glue laminated beams, laminated veneer lumber (LVL), or Microlam.RTM. Parallam.RTM., laminated strand lumber (LSL), and by other names. EWP members are differentiated in the art from panel type products such as plywood, oriented strand board (OSB), particle board and the like. The EWP can be manufactured to any length, offering an advantage over normal wood members which are limited in length by the size of available raw wood. The solid wood flanges are typically woven together with glue at periodic finger joints. For convenience in shipping, the EWP members are usually manufactured at lengths of 40, 48 and 60 feet.
Unfortunately, the added length of the EWP members is inconvenient to handle when cutting to size for a production site. The added length makes accurate length measurement by a conventional measuring wheel assembly difficult and slows production when using a push-foot type feeder system. The EWP member typically is cut into several lengths, or cut members, for use at a site. The length of the cut members often must be accurate to within one-quarter inch of the desired length. While small inaccuracies in length measurement may not cause a significant variance when measuring a shorter conventional wood member, the cumulative effect of such measurement inaccuracies over the length of the longer EWP members may result in unacceptable length variances.
One type of error in measuring the length of an EWP member can be caused from measuring an EWP which is bent, bowed or otherwise misshapen. Inaccuracies in measurement by a wheel measurement assembly may be caused by imperfections in the wood and by the type of measuring wheel employed. The flange members of the I-beam type EWP will naturally include imperfections such as hard and soft spots, knots, voids, bends and the like. A typical wheel measurement assembly employs a measuring wheel having a knurled, serrated or spiked surface. The knurls assist the wheel in maintaining a constant friction with the wood surface. Unfortunately, the knurls will tend to bite into the wood in the soft spots and simply ride along the surface in the hard spots and at knots, causing the measuring wheel to travel vertically with respect to the wood surface. Similar motion of the wheel is caused where a void or bend in the wood member causes the entire wheel to "sink" towards the member as it rolls on the surface of the wood. This vertical motion results in inaccurate measurements. The distance the wheel has turned is the horizontal length of the wood member being measured plus the vertical distance traveled by the wheel dug measurement. The imperfections in the wood may cause only slight movement of the wheel in the vertical direction, fractions of an inch, but the sum of the vertical movement over the length of a sixty foot EWP may be significant.
This problem may be exacerbated by the characteristics of the measuring wheel itself Where the knurls or spikes are long, the wheel may sink and rise the length of the spikes creating measuring inaccuracies. This may be the case where the serrations are as small as 0.002 inches. Further, the size of the measuring wheel may cause problems. If the wheel is small, the wheel will tend to ride up and down on a great many of the imperfections in the wood thereby increasing the error in the length measurement.
Another problem presented by the great length of typical EWP members is slowed production speeds. When measuring and cutting conventional wood products, often a pushfeed mechanism is employed wherein a pusher foot, powered through a belt or pulley to slide along the length of the infeed table, engages the EWP and pushes the member into the measuring and cutting stations. The rear feed system provides for accurate measurement since the positioning of the pusher foot itself can be accurately measured, but after feeding a member through the measuring station, the pusher foot is "reset", or returned, to its original position away from the measuring and cutting units. For the longer EWP members, the pusher foot would need to travel 40 to 60 feet to its original position slowing production speeds.